Some objects are intentionally radiated with ionizing radiation, such as X-rays and Gamma-rays. For example, medical devices may be radiated for sterilization purposes, food may be radiated to remove microorganisms (e.g., E. coli bacteria), and luggage may be radiated as it moves through security at an airport. However, ionizing radiation may be undesirable in other situations.
Regardless of whether the ionizing radiation is beneficial or not, a radiation sensor may be used to detect whether radiation has occurred or not. If radiation has occurred, some radiation sensors may also determine the amount or dose of radiation to which an object has been exposed. Typically, a radiation sensor is placed on or near the object or person likely to be exposed to radiation.
Thermoluminescent devices (TLDs) and chromatic tags are common radiation sensors. TLDs may generally be described as crystals, e.g., lithium floride, whose structure changes during exposure to radiation. More particularly, during irradiation, electrons travel to and are trapped in the crystal after being ejected by the high-energy (ionizing) photons used for sterilization. Upon exposure to heat, the electrons in the crystal fall back to their ground states and emit light as result of the change. A spectrophotometer measures this light and provides a quantitative assessment of the amount of radiation to which the device was exposed. A technician typically recovers the TLD from an irradiated package and then analyzes/measures the emitted light on the spectrophotometer. Unfortunately, this process can be relatively labor-intensive and can be undesirable for use in a mass production environment.
Chromatic tags may generally be described as plastic tags that undergo a color change upon exposure to radiation at some level. A technician may visually evaluate the color change. Colormetric readers may also be used to quantify the color change to a more exact level. Unfortunately, again, the determination of the dose measured in this manner can also be labor intensive and/or unsuitable for a mass-production environment.
Some radiation sensors use circuits that react in a measurable way to ionizing radiation. For example, a tank circuit may be used as a radiation sensor. When the tank circuit is exposed to radiation, the radiation affects the operational properties of the tank circuit and these changes may be transmitted to a remote detection circuit, which can then determine the radiation dose. The detection circuit is located at a remote location so that this circuit is not impacted by the radiation. While these sensors are more suitable for mass-production, they are typically single use, disposable sensors.
As a radiation sensor may have many applications and be required in large quantities, it would be beneficial to have a sensor that is inexpensive, compact, noninvasive, and operates passively, i.e., requires no power to detect radiation. Moreover, it would beneficial to provide an ionizing radiation sensor and associated detection circuitry in a single package.